There are many designs of fluid dispensers or combinations mixer-dispenser shown in the prior art. The majority of the designs employ, in essence, a method to increase the static pressure in the multi-chambered reservoir where the fluids to be dispensed are stored, and a metering method for controlling the amount of fluid being dispensed. The dispensed fluid is expelled out of the reservoir through an orifice (nozzle) into a container or mixing chamber. The dispenser designs based on static pressure increase include syringe or piston type as disclosed in the U.S. Pat. Nos. 4,848,606; 5,862,947; 6,682,601; 5,348,585; 6,402,364; 6,550,643; and 6,719,170 or pump type as disclosed by U.S. Pat. Nos. 5,366,117; 5,816,445; 4,871,262; and 4,790,456, which can have various driving forces such as manual, mechanical, pneumatic, or hydraulic. Another dispensing method, applicable to some substances, rely on an auger screw to push out the substance being dispensed. Many of the prior art dispensing methods lack the capability to conveniently dispense viscous or fast drying substances in small and precise quantities. The dispensers based on prior art that attempt to dispense these types of substances have to be often cleaned in order to maintain functionality and accuracy, which is time consuming and inconvenient.
A widely spread dispenser based on static pressure increase can be found in almost all paint stores. It is being used for creating custom colored paints. The dispenser has a user interface and is computer controlled. The user can select a color from the computer's database or the customer can bring a sample of the desired color which is scanned, identified, and then a color formulation is produced by the computer. Even though in most cases the paint dispenser produces acceptable results for paint quantities down to 400 ml, the dispenser is not capable to produce color paint mixes in smaller quantities. A typical problem of dispensers based on static pressure increase, such as the color paint dispenser, is residual dispensing or leakage of extra fluid after the intended amount of fluid has been dispensed. The accuracy, controllability, dispensing capability, and reliability of the various dispensers vary substantially based on their designs. Typically, the dispensers which are more sophisticated have greater capabilities and are more accurate and reliable, but they are also more complex and much more expensive.
Yet, another dispensing method is represented by the ink jet printer type of dispensers which can have different driving methods such as piezo-electric, heating elements, or others, as disclosed in the U.S. Pat. No. 6,715,642. A problem with the ink jet printer type of dispensers is that they are only capable of dispensing a series of very small droplets which results in longer time to produce a usable quantity of cosmetics and the method is not suitable for substances that contain fast evaporating solvents.
Cosmetic fluids pose unique challenges and have special requirements for dispensing. The majority of the cosmetic substances are designed to have good wetting properties and to be sticky. Cosmetics typically have high viscosities and also include a solvent or volatile component which evaporates after application. Therefore, any residue left on the parts of the mechanism after dispensing, will solidify due to the evaporation of the volatile component and most likely make the mechanism lose its accuracy or become non-operational. The dispensing mechanism needs to be able to dispense substances like nail polish which dry-out in a few seconds. Additionally, a dispenser designed for cosmetics needs to protect the fluid from air exposure since some cosmetic substances, such as hair dyes, can oxidize in air and need to be sealed-off until usage. A dispensing mechanism for cosmetic substances needs to be able to address all these issues and also be capable to accurately dispense small volumes, down to micro-liter size. None of the dispensers based on the prior art can satisfy all of these requirements.